Convex Mirror, Principal Ray Diagram

We know that not only a plane mirror produces an image of an object in front of it – a convex spherical mirror does, too! Just look at the back of a metal spoon if you don't believe it!

This interactive animation shows you how such an image arises, and how its position and size can be found. Use your mouse to move the object, the candle, along the optical axis, and observe how the position and size of its image change.

You can also explore how the image is constructed, by turning on and off the principal rays. These are the three special rays that are used for the construction of the image. The first one is parallel to the optical axis and is therefore called the P-ray. It is reflected as if it came from the focal point of the mirror. The second one is the one that goes through the center of the sphere, the C-ray, which is reflected back into itself. The third is the F-ray, which would go through the focal point and is reflected parallel to the optical axis. The image of the tip of the candle is the point where these rays meet (or seem to meet) after they were reflected.

It might not come as a surprise that the image of the candle is actually located behind the convex mirror, so it's a virtual image. The reflected rays to not actually meet at the position of the image, they just emerge from the mirror as if they came from there. Of course, that's the same as with a plane mirror. But you'll notice that there is also a difference: the image of a plane mirror is the same size as the object, while for a convex mirror, the image is always smaller than the object.  

 

 

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